Allow me to paint a scenario. Oriko sees black feathers, and the idea of meeting Sabrina again even after she is gemsmashed.
Riona, for whatever reason, decides to steal Oriko's soul and try to hurt us. "I want your power," let's say. Riona steels Oriko's soul and Oriko's Shade blocks her own visions in the past.
Riona proceeds to steal the souls of everyone else Oriko predicted seeing dead with no injuries of any kind, which includes Sayaka, Homura, and Madoka at least.
Riona having those powersets is super dangerous, and also paints a pattern of "I killed and enslaved all your friends. If you want their souls back, surrender."
If there's anything I can think of that would actually make Sabrina flip the fuck out and Witch Out/kill someone, it's that. If anything can make Sabrina griefspiral and witch out, it's that.
In this hypothetical future, Riona creates Dedolere, who uses its grief-control to control Irkalla, and thus her powers, and thus absorb everyone's souls and powers.
Bad shit happens.
Dedolere, either to create herself in a timeloop or to prevent this future, uses Homura's magic to reach back in time, and uses Riona's magic to meld all these stolen souls together into one soul that knows everything Sabrina knows, and has all of her potential by way of being Madoka+others.
Dedolere creates Sabrina, a construct created out of the souls of all her dead friends, as a way of saving them/changing the future.
Feathers, explained.